JPS6281813A - Phase shift circuit - Google Patents

Abstract

PURPOSE:To obtain a circuit keeping a specific phase relation with an input signal regardless of a frequency by deciding the phase shift of a variable phase shifter depending on the frequency detected by a frequency detection circuit. CONSTITUTION:The input signal is compared with a variable frequency oscillator (VCO) 3 by a phase comparator 1 and its output is impressed to a control terminal of the VCO 3 via a loop filter 2'. Other output signal extracted from a part of the loop filter 2' is used as a control signal to control the phase quantity of a variable phase shifter 4' to shift the phase of the output signal of the VCO 3. The phase shift quantity is set by storing an optional relation into ROMs 18a, 18b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a phase shifting circuit in a circuit including a single frequency signal generation mechanism, such as a PLL circuit.

[Technical background of the invention and its problems]

Taking a PLL (7-speed lock loop) as an example, a configuration as shown in FIG. 2 has conventionally been used. That is, the input signal is sent to the phase comparator (1) to generate a phase error signal with respect to the reference signal, and then passed through the loop filter (2) to the VCO (3)? Control.

The output of the vCO is divided into two branches, one of which is supplied as a reference signal to a phase comparator, and the other of which is converted into an output signal having a desired phase by a suitable phase shifter (4). 5.) is a so-called localization type filter, largely because it was implemented using analog elements.
The variable range of VCO was naturally limited to a narrow range.

In recent years, with the advancement of digital technology, cases have arisen in which non-localized loop filters are constructed using digital elements and applied to the circuit shown in FIG. 2.

In such a case, the variable range of the VCO can be made much wider than in the past. Then, conventionally.

The phase of output No. 1 was fixed at a desired value by the phase shifter (4), but due to the electrical length of the output cable (5), etc. present in the output part of the circuit, the phase changes depending on the oscillation frequency of the VCO. starts rotating.

This is extremely inconvenient in a circuit whose purpose is to obtain an output signal that has a specific phase relationship with the input signal.

[Purpose of the invention]

The present invention is intended to improve the drawbacks of the conventional circuit described above, and even when the circuit includes cables having a large electrical length,
It is an object of the present invention to provide a phase shift circuit that obtains an output signal that maintains a specific phase relationship with an input signal regardless of the oscillation frequency of the CO.

[Summary of the invention]

The present invention considers the disadvantages of the operation of the circuit shown in FIG. The idea was to control the That is, it has a frequency detection circuit and a variable phase shifter, and the amount of phase shift of the variable phase shifter is determined by the frequency detected by the frequency detection circuit.

[Effects of the Invention] According to the present invention, for example, a PLL circuit with a wide lock range can be realized regardless of the electrical length.

Further, even in the case of a circuit including a filter or the like in which the phase difference varies depending on the frequency, by using a digital circuit, it is possible to obtain an output signal that always maintains a constant phase relationship with the input signal.

Ru.

Frequency information can be easily output when the loop filter is composed of digital elements, and even when the loop filter is composed of analog elements, it can be easily obtained by simply adding a simple low-pass filter. I can do it.

[Embodiments of the invention]

Embodiments of the present invention will be described with reference to the drawings.

The tenth is the case where the present invention is applied to the P T, L circuit [1
This is a perfect example. The input signal is phase-compared with the basic signal by a phase comparator (+1) to generate a total phase error signal.

The phase error signal is input to the loop filter (2'),
Two output signals are generated. One output signal is.

One signal controls vCO as obtained in the conventional PLL circuit as shown in FIG. 2, and the other signal controls the amount of phase shift of the variable phase shifter (4').

The above configuration can be realized by a digital circuit as shown in FIG. 3 in more detail.

The phase comparator (1) is an example of a quadrature demodulator, as shown in the figure, A
/D converter and Memo IJ (PC40M).

As shown in the figure, the loop filter (2') inputs the phase error in digital form from one phase comparator, and is a well-known fully integral type digital filter circuit and a D circuit that converts the digital filter output into an analog signal. /A converter. The reason why the D/A conversion is performed here is because it is common to use RICO'2 and an analog signal is required as its control signal.

As shown in the figure, the phase shifter 4' is composed of a ROM, a D/A converter, and a quadrature modulator. The contents of the two ROMs are
When the amount of phase shift corresponding to the frequency information outputted from the frequency register in the loop filter is φ, each 5IN(
φ), an amount proportional to C08(φ).

By using a ROM as in this embodiment, it is possible to create an arbitrary relationship between the frequency and the amount of phase shift.

For example, the phase delay of a signal passing through a general cable increases linearly as the frequency increases, but with the fifth embodiment, not only can this be reversed, but also the phase delay increases linearly as the frequency increases.
Furthermore, any relationship such as a non-linear relationship can be provided.

This is an extremely effective characteristic, for example, when canceling the phase characteristics of an output cable where reflection occurs.

[Other embodiments of the invention]

The embodiments so far have explained the implementation of the present invention in a PLL circuit, but the present invention can also be applied to 5 other applications, such as PLL circuits.
The present invention can also be applied to the tank portion of an inverse modulation tank limiter circuit used for SKS decoding. Particularly when the tank circuit has an AFC function, by fully implementing the present invention, it is possible to realize a tank circuit that operates satisfactorily over a wide band. The present invention can be implemented with a configuration as shown in FIG.

Furthermore, with the configuration shown in FIG. 5, the present invention can be implemented in a quadruple multiplier circuit that performs gear rear reproduction of a four-phase modulated wave.

Furthermore, with the configuration shown in FIG. 6, the present invention can also be implemented in a remodulation PLL type four-phase phase modulated wave demodulation circuit. In this embodiment, frequency information is obtained by passing the loop output filter output through a low pass filter. Furthermore, by implementing the present invention, it is possible to correct the electrical length of the delay circuit (44) in the remodulation circuit in addition to the cable (5).

[Brief explanation of drawings]

FIG. 1 is a diagram showing a circuit configuration of an embodiment of the present invention, and FIG. 2 is a diagram showing a circuit diagram of a conventional example. 3 to 6 are detailed circuit configuration diagrams in five embodiments of the present invention. 1... Phase comparator 2.2'... Loop filter 3... VCo 4.4'... Phase shifter 5... Output cable 1
0... Orthogonal demodulator 11a, b... A/D converter 12... Phase comparison ROM 13.14... Coefficient circuit 15... Cumulative addition circuit 16... Adder 17
．． 19a, b...-D/A converter 19a, b...
・-ROM 20... Quadrature modulator Fig. 2 Fig. 3 Fig. 4

Claims (4)

[Claims] (1) A phase shift circuit comprising a frequency detection circuit and a variable phase shifter, the phase shift amount of the variable phase shifter being determined by the frequency detected by the frequency detection circuit; (2) The frequency detection circuit consists of a reference oscillator, a quadrature demodulator, and a digital filter, the output of the reference oscillator is inputted to the quadrature demodulator together with the input signal, and the output of the quadrature demodulator is digitized and output to the digital filter. 2. The phase shift circuit according to claim 1, wherein the digital filter outputs frequency information of the input signal. (3) The variable phase shifter uses the output signal of a variable frequency oscillator (VCO) as an input signal, and the output signal of the frequency detection circuit controls the frequency of the variable frequency oscillator. Phase shift circuit described in section. (4) The variable phase shifter uses the output signal of the variable frequency resonant circuit as an input signal, and the output signal of the frequency detection circuit controls the resonant frequency of the variable frequency resonant circuit. Phase shift circuit described in section.